PTO Shaft Issue with Shear Bolt

[Neophyte]

Thanks for the chart! I will cross-reference it with my manual, if I get one.

Cuz if/when a smoothbore slip clutch freezes up from neglect, you've automatically defaulted to a shear bolt configuration again.

Isn't this a good thing? At least it is falling back onto a Grade 5 shear bolt. With a spline shaft, you would have no additional protection in the case that the slip clutch seizes.

 

[greg_g]

Isn't this a good thing? At least it is falling back onto a Grade 5 shear bolt. With a spline shaft, you would have no additional protection in the case that the slip clutch seizes.

I don't consider it a good thing. Among other things it still leaves you vulnerable to bolt hole damage. Then there's also the chicken and egg question of which can/will take more torque - the clutch or the bolt? Conversely, which will give first? Remember I said that in the smoothbore type, all the torque is initially transferred to the bolt - which in turn transfers it to the section of shaft that's got a hole in it. In the spline type, torque is delivered directly along the entire mating surface of the input transmission shaft.

//greg//

 

[Neophyte]

I just received my slip clutch from Agri-Supply.

The sticker on the slip clutch says to use "GRADE 8 BOLTS ONLY" on the gear box and driveline connections. I think I will use Grade 8 on the gear box side but I may still use a Grade 5 on the driveline side.

There was no manual or instructions included, which is odd. I'm still left wondering how to maintain it properly.

 

[Soundguy]

A couple observations..

1, Wow.. now that's a twisted shaft...

2, I think I'd have rather popped another grade 2 bolt than bent the shaft.

3, I think i'd have chipped for a bigger shaft...

4, 1.5' woody, and 2" green is usually safe for occasional cutting.. and 2" woody for extremly limited cutting... That 4" - 6" fiberous stump where all the branches converged to.. well.. you don't need to be brush hogging those kind of things...

I've accidentally cut a 3" semi-woody/green sappling tree down when it caught the corner of my hog and got sucked under... Sounded like a plane crashing for a few seconds untill the tree carcass got rolled out the back... I had a slip clutch, and glad i did.. i don't intentionally try to cut 3" material...

Soundguy

I know I'm going to get alot of "I told you so's" but I wanted to share this for others that may be considering it.

My 3320 is a 32.5 HP tractor with 25 PTO HP.

My Howse 500 has a 55 HP gearbox and is recommended for a 25-45 HP tractor. Without a slip clutch, Howse recommends a Grade 5 bolt and it even says so on their website. Click on Z62, it's a Grade 5 bolt. I was never able to confirm this in their manual since I have been waiting several weeks for one and I still don't have it. Have I mentioned that Howse's customer service is terrible?

Howse Model 300, 350, 400 & 500 Parts Breakdown

So I purchased a new PTO driveshaft for my 5' rotary cutter at a local dealer. I gave them my tractor HP, PTO HP, and implement specs. They recommended a Tisco P/N AB4111WY. You can see the details by entering that P/N at this link.

Tisco Parts Catalog

It is a 4 series PTO shaft, which is rated for 35 HP & 460 Nm (torque) at 540 RPM. You can see additional details at this link.

PTO Specifications and Information

Despite the fact that Howse recommends a Grade 5 shear bolt, I was using Grade 2. However, they were popping way to easy and way too often. After I ran out of about 15 Grade 2 bolts (seriously), I decided to go with their Grade 5 recommendation. I have attached the results.

I noticed the problem when I went to collapse the PTO shaft and it would not collapse completely. I was hoping that it was a burr or dirt but I knew without looking that it was twisted. Removing the safety cover confirmed this.

I supposed it could have been worse. I could have damaged my RC gearbox or tractor PTO.

If my tractor is only 25 PTO HP, should a 35 HP PTO Shaft twist like this?

I was talking to someone about this and he said this is why you want to run at 540 RPM. He said that when running at lower RPMs, you are running at higher torques, which can damage things such as PTO shafts. Is this true?. It's a moot point though because I was running at 540 RPM the entire time.

I was reading online that typically a 5 series PTO shaft (48 HP & 620 Nm) is used for rotary cutting applications. Should I have purchased a 5 series instead of the 4 series? My dealer said that all his new Woods and Bush Hog rotary cutters are being supplied with 4 series drive shafts.

Needless to say, I just purchased a slip clutch at Agri-Supply for $63 plus S&H. I was given a price of $150 locally. This works out nicely because of the added length of the slip clutch. I will be able to un-pin the twisted shaft, cut the twisted portion out, drill it and re-pin it. The reduced length will make room for the new slip clutch and I won't need to purchase a new shaft.

Agri-Supply Slip Clutch

I still think that a shear bolt (Grade 2) is fine for field mowing. However, if you are mowing through thick brush like I am, then I think a slip clutch is a necessity.

Should I be using a Grade 5 or Grade 8 bolt on the slip clutch shaft holes?

Given the fact that you can't use a C-Ring to hold the slip clutch on to the gearbox shaft, I would think you would want a Grade 8 bolt on this side to ensure that it never shears. I think the slip clutch allows for a C-ring on the PTO shaft side. Given this, my guess would be to use a Grade 8 bolt on the gearbox side of the slip clutch and a Grade 5 bolt on the PTO shaft side.
.

 

[Farmwithjunk]

The new slip clutch should come with an instruction sheet, but that's not a given. If not, the chart I uploaded might help. Be careful though, these spring lengths only apply to the 55hp rated clutch. Confirm the PTO horsepower rating of your tractor, consult the chart, adjust the spring length accordingly.

LIke I said before, I purposefully select implements/clutches that have splined shafts and receivers. The type that just bolts to a smooth transmission input shaft needs a lot more attention. That is; at least semi-annual disassembly cleaning, spring adjustment. Cuz if/when a smoothbore slip clutch freezes up from neglect, you've automatically defaulted to a shear bolt configuration again.

//greg//

Just be careful when adjusting any slip clutch to know the CORRECT spring stack height for YOUR clutch. I bought a new Bush Hog 286 cutter last winter. The manual list's 2 different brands of clutches as possibilities to be installed on that model. In addition, one brand had 2 different designs available. And all that was for a specific HP rated clutch. The possibilities are endless as far as correct adjustments. (Stack height's varied as much as 1/4" between different brands to achieve same end results)

 

[Neophyte]

I didn't get a manual or any instructions with the slip clutch. I checked the manufacturers website but I couldn't find anything. I contacted Agri-Supply to see if they had anything but I have yet to hear from them.

I believe it is manufactured by Eurocardan but I'm not positive.

 

[Soundguy]

If it is eurocardan.. find a dealer and check their locations... I know TSC carried some eurocardan shafts.. but not sure if their slip clutches are EC or if they are SPEECO..

Soundguy

 

[greg_g]

I believe it is manufactured by Eurocardan but I'm not positive.

That spring length chart I uploaded is from Eurocardan. But again, it's for the 55hp splined shaft version - they actually make at least 7 variants. Consider that if/when you refer to it for adjusting your spring length to match tractor PTO hp

If it helps, there catalog is at http://www.eurocardan.it/documenti/Catalogo_prodotti.pdf. Slip clutches are in the section that starts about pg40. Having said that, they all appear to be splined on the female end. SpeeCo though, I don't think I've ever seen a slip clutch from them. Over-running clutches, yes. slip clutches, ??

//greg//

 

[Tom_Veatch]

He said that when running at lower RPMs, you are running at higher torques, which can damage things such as PTO shafts. Is this true?. .

Yes, assuming the power output is the same in each case. But that is probably an incorrect assumption for a given task.

To develop a given power at a slower shaft speed, a higher torque is required. That doesn't mean that slower speeds always mean higher torque. You have to consider the application.

Often, a task requires a given torque (or force) and "power" only affects how fast you accomplish that task. For example, lifting a hundred pound sack of feed at a constant speed requires 100 pounds of force, no more, no less. Neglecting the force required by the initial acceleration, the force required to lift the sack won't exceed 100 pounds no matter how much power is applied. But, the more power you have available, the faster you can lift the sack.

Linear Speed X Force = Torque X Rotational Speed = Power

Note, however, in starting up from a stopped, non-moving condition, you may not can safely neglect the acceleration forces/torques depending on how rapidly you apply the forces/torques.

 

[gclark94560]

Hi! New member Greg Clark here.

I was just about ready to by a over running coupler for my YM2000 until I read this thread. I really see the value in a clutch for my 4' bush hog.

Is it possible to use both? Perhaps one on each end of the shaft?

I am a bit concerned by the bush hog continuing to drive the tractor forward when I push in the clutch. It makes it a safety issue if I need to slam on the breaks becuz I see I am about to mow a stump hiddenig the weeds!

Greg